A variety of diseases exist which require regular treatment by injection of a medicament. Such injection can be performed by either medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses once or several times per day. It is known to couple a supplemental device to an insulin injection device for recording information about the doses which are administered. Supplemental devices may be used to record dose history information such as the various times at which insulin is administered and the quantity of insulin administered at each such time.
Although electronically recording dose history information addresses the problem of inaccurately recording such information manually, it has the disadvantage of providing a false representation of how much medicament a patient actually injects themselves with. In particular, before administering an injection a patient may eject a small amount of medicament in a so-called prime shot to remove air from within their needle. Supplemental devices configured to record how much medicament is ejected from an injection device will record both amounts of medicament ejected during prime shots in addition to amounts of medicament that are actually injected into a patient. It will thus be appreciated that simply recording how much medicament is ejected from an injection device does not give an accurate determination of how much medicament is actually injected into a patient. Not knowing such information within an acceptable degree of tolerance may have potentially serious consequences if a patient is subsequently over or under prescribed medication on the basis of an incorrect understanding of how much medicament has previously been injected.